Air conditioning is used worldwide to provide comfortable and healthy indoor environments that are properly ventilated and cooled and that have adequate humidity control. While being useful for conditioning supply air, conventional air conditioning systems are costly to operate as they use large amounts of energy (e.g., electricity). With the growing demand for energy, the cost of air conditioning is expected to increase, and there is a growing demand for more efficient air conditioning methods and technologies. Additionally, there are increasing demands for cooling technologies that do not use chemicals and materials, such as many conventional refrigerants, that may damage the environment if released or leaked. Maintenance is also a concern with many air conditioning technologies, and, as a result, any new technology that is perceived as having increased maintenance requirements, especially for residential use, will be resisted by the marketplace.
Evaporative coolers are used in some cases to address air conditioning demands or needs, but, due to a number of limitations, conventional evaporative coolers have not been widely adopted for use in commercial or residential buildings. Evaporative coolers, which are often called swamp coolers, are devices that use simple evaporation of water in air to provide cooling in contrast to conventional air conditioners that use refrigeration or absorption devices using the vapor-compression or absorption refrigeration cycles. The use of evaporative cooling has typically been limited to climates where the air is hot and humidity is low such as in the western United States. In such dry climates, the installation and operating costs of a conventional evaporative cooler can be lower than refrigerative air conditioning. Residential and industrial evaporative coolers typically use direct evaporative cooling with warm dry air being mixed with water to change the water to vapor and use the latent heat of evaporation to create cool moist air (e.g., cool air with a relative humidity of 50 to 70 percent). For example, an evaporative cooler may be provided in an enclosed metal or plastic box with vented sides containing a fan or blower, an electric motor to operate the fan, and a water pump to wet evaporative cooling pads. To provide cooling, the fan draws ambient air through vents on the unit's sides and through the dampened pads. Heat in the air evaporates water from the pads, which are continually moistened to continue the cooling process. The cooled, moist air is then delivered to the building via a vent in the roof or a wall.
While having an operation cost of about one fourth of refrigerated air conditioning, evaporative coolers have not been widely used to address needs for higher efficiency and lower cost conditioning technologies. One problem with many sump coolers is that in certain conditions these evaporative coolers cannot operate to provide adequately cooled air. For example, air may only be cooled to about 75° F. when the input air is 90° F. and 50 percent relative humidity, and such cooling may not be adequate to cool a particular space. The problem may get worse as temperatures increase such as to temperatures well over 100° F., as found in many locations in the southwest portion of the United States and elsewhere. As a result, the air conditioning system may need to include refrigerated air conditioning to cool the outlet air from the evaporative cooler, which results in a system that is more expensive to purchase, operate, and maintain.
Additionally, conventional evaporative coolers provide no dehumidification of the air and, in fact, often output air at 80 to 90 percent relative humidity, which may only be acceptable in very dry environments as very humid air reduces the rate of evaporation for occupants of the building (e.g., reduces comfort levels) and can cause condensation resulting in corrosion or other problems. Dehumidification is provided as a second or later stage in some evaporative coolers such as by wicking a liquid desiccant along a wall of the air flow channel or chamber, but such systems have not been widely adopted due to increased operating and maintenance costs and concerns of having the desiccant expelled with the conditioned air. In general, maintenance is a concern with conventional evaporative coolers as the evaporation process can result in mineral deposits on the cooling pads and other surfaces of the cooler that need to be cleaned or replaced to maintain the efficiency of the system, and the water supply line needs to be protected against freezing during the off season such as by draining the system. Due to these and other concerns, conventional evaporative cooling is unlikely to be widely used to provide an energy efficient, air conditioning alternative for commercial and residential applications until significant improvements are made that address maintenance concerns while improving achievable cooling (e.g., providing adequately cooled output air for direct use in a building).
The foregoing examples of the related art and limitations related therewith are intended to be illustrative and not exclusive. Other limitations of the related art will become apparent to those of skill in the art upon a reading of the specification and a study of the drawings.